SYNERGISTIC ACTIONS OF INTRAVENOUS ANESTHETICS

描述（由申请方提供）：γ-氨基丁酸A型（GABAA）受体是递质门控离子通道的Cys环家族成员。受体对突触释放的或周围的递质作出反应，产生构象变化，导致门打开，允许离子运动通过通道。GABAA受体活性的增强是许多静脉麻醉剂（如依托咪酯和丙泊酚）的麻醉作用的基础。虽然没有在积极的临床使用，神经活性类固醇是GABAA受体的最有力和有效的增效剂之一。丙泊酚、依托咪酯和神经活性类固醇也直接激活GABAA受体，尽管直接激活的浓度通常高于引起增强的浓度。我们的初步数据表明，一些神经活性类固醇强烈加强门控异丙酚或依托咪酯。低浓度的GABA与低浓度的类固醇的组合导致增强程度的显著的超加和增加。在蝌蚪和小鼠的行为测定中，存在一个低的，阈下浓度的增强类固醇的结果在翻正损失的剂量-反应关系中的一个显著变化，而在细胞系中，类固醇的存在并不影响依托咪酯引起的皮质醇释放抑制。本工作的总体目标是确定类固醇类似物和静脉麻醉药对GABAA受体的相互作用机制，并探讨这些发现的临床意义。我们将：i）检查类固醇与变构激活剂对异源表达系统中表达的重组突触和突触外GABA的协同作用; ii）检查类固醇和静脉内麻醉剂在蝌蚪和小鼠行为测定中的协同作用的行为后果;和iii）探测在类固醇存在下产生镇静所需的麻醉剂的降低剂量是否导致脱靶效应降低。这些目标的完成将增加我们对GABAA受体在健康和疾病中如何发挥作用的理解，并为未来开发新的治疗方法奠定基础。

DESCRIPTION (provided by applicant): The γ-aminobutyric acid type A (GABAA) receptor is a member of the Cys-loop family of transmitter-gated ion channels. The receptors respond to synaptically-released or ambient transmitter with a conformational change, resulting in the opening of the gate that allows ion movement through the channel. Potentiation of GABAA receptor activity underlies the anesthetic effects of many intravenous anesthetics, such as etomidate and propofol. Although not in active clinical use, neuroactive steroids are among the most potent and efficacious potentiators of the GABAA receptor. Propofol, etomidate and neuroactive steroids also directly activate the GABAA receptor, although the concentrations for direct activation are typically higher than those that cause potentiation. Our preliminary data demonstrate that some neuroactive steroids strongly potentiate gating by propofol or etomidate. Combination of a low concentration of GABA with a low concentration of steroid results in a remarkable, supra-additive, increase in the extent of potentiation. In tadpole and mouse behavioral assays, the presence of a low, subthreshold concentration of a potentiating steroid results in a leftward shift in the dose-response relationship for loss of righting whereas in a cel line the presence of a steroid does not affect etomidate-elicited suppression of cortisol release. The overall goal of the present work is to determine the mechanism of interactions of steroid analogues and intravenous anesthetics on GABAA receptors, and to explore the clinical significance of the findings. We will: i) examine the synergistic effects of steroids with allosterc activators on recombinant synaptic and extrasynaptic GABA expressed in heterologous expression systems; ii) examine the behavioral consequences of synergistic effects of steroids and intravenous anesthetics in tadpole and mouse behavioral assays; and iii) probe whether reduced doses of anesthetics required to produce sedation in the presence of steroids lead to reduced off-target effects. The completion of these aims will increase our understanding of how the GABAA receptor functions in health and disease, and lay a foundation for future development of novel therapeutic approaches.